This invention relates to apparatus for use in downhole operations. In particular, but not exclusively, the apparatus relates to an isolation valve intended for use in completion testing and in operations which take place immediately following completion testing.
In the oil and gas exploration and extraction industries, deep bores are drilled to gain access to hydrocarbon-bearing strata. The section of bore which intersects this strata or xe2x80x9cproduction zonexe2x80x9d is typically provided with a steel xe2x80x9clinerxe2x80x9d, while the section of bore extending to the surface is lined with steel xe2x80x9ccasingxe2x80x9d. Oil and gas is extracted from the production zone through production tubing extending through the casing from the upper end of the liner. The production tubing is formed of a string of threaded sections or xe2x80x9csubsxe2x80x9d which are fed downwards from the surface, additional subs being added at the surface until the string is of the desired length. As the string is assembled and fed into the bore its pressure integrity, or xe2x80x9ccompletionxe2x80x9d, is tested at regular intervals. Such testing is also carried out on the complete string. The testing is accomplished by pressurising the internal bore of the string. Of course this requires that the string bore is sealed at its lower end.
This sealing of the string bore is generally accomplished using a valve or plug which will normally remain closed or in place once testing is completed, to allow the packers mounted on the string to be set to locate and seal the string within the casing or liner. The valve or plug may then be opened or removed to permit formation fluid to flow upwardly to the surface through the production tubing. The opening or removal operation generally requires running in of an appropriate tool on, for example, wireline or coiled tubing, which will involve additional time and expense.
It is among the objectives of embodiments of this invention to obviate or mitigate these disadvantages. It is a further objective of embodiments of this invention to provide an isolation valve which will hold pressure in two directions, that is from the sump side and the surface side.
According to a first aspect of the present invention there is provided a downhole valve comprising a body defining a bore, a valve closure member positioned in the bore, first and second retaining members positioned on respective sides of the valve closure member for retaining the valve closure member in a closed position and to hold pressure from both sides, one of the retaining members being retractable to permit opening of the valve closure member.
In use, such a downhole valve will hold pressure from both the surface side and the sump side. The terms xe2x80x9cabovexe2x80x9d and xe2x80x9cbelowxe2x80x9d are used herein, but those of skill in the art will of course realise that the invention may be used with equal utility in inclined or horizontal bores, and the orientation of the valve may be varied.
Preferably, with the valve closure member in the open position, the body defines a slick bore.
Preferably also, the valve closure member comprises a flapper in the form of a disc. Most preferably, the disc is in the form of a curved or concave disc. In the preferred embodiment a convex surface of the disc engages a valve seat.
Preferably also, one of the retaining members is extendable to maintain the valve closure member in an open position and to provide a slick bore. In the preferred embodiment one of the retaining members is both retractable, to permit opening of the valve closure member, and extendable to maintain the valve closure member in the open position.
Preferably also, one of the retaining members incorporates a valve seat. The valve seat may include an elastomeric seal located in an end surface of the retaining member. Most preferably, the retaining member incorporating the valve seat is non-retractable. Alternatively, a separate valve seat may be provided.
Preferably also, the retractable retaining member is moveable by application of fluid pressure thereto. The fluid pressure may be provided by well fluid in the borehole, and most preferably by the well fluid in the body bore. The supply of fluid from the body bore to actuate the retaining member may be controlled by an appropriate valve, such as described in PCT/GB95/02046.
Preferably also, the retractable retaining member includes a sleeve portion defining a piston, such that application of fluid pressure between the sleeve portion and the body tends to retract the member from a retaining position. The member may be biassed towards the retaining position by biassing means, such as a spring.
Preferably also, the retractable retaining member is lockable in the retaining position, but is releasable, most preferably on application of actuating fluid pressure. Most preferably, the unlocking of the retractable retaining member is controlled by a ratchet assembly comprising first and second axially relatively movable parts, each part defining a toothed face, and a ratch member located between the toothed faces, pressure induced reciprocal movement of the parts advancing the ratch member axially along the toothed face of the first part, in an advanced position the ratch member engaging a unlocking member such that further movement of the first part actuates the unlocking member to release the retaining member.
Additionally, or alternatively, the retractable retaining member may be releasable by application of physical force by a further tool located in the bore. Preferably, the unlocking member defines a tool engaging profile for cooperating with said further tool.
Preferably also, the retractable retaining member may be latched in the retracted position, to permit opening of the valve closure member, and then released to return to an extended position to maintain the valve closure member open.
Preferably also, the valve closure member is in the form of a flapper and is mounted on a valve carriage which, with the retaining member retracted, is axially movable towards the retaining member such that the retaining member may contact the flapper and push the flapper towards the open position. The valve carriage and the retaining member are preferably connected by a resilient link. In the preferred embodiment, retraction of the retaining member is achieved by pressurising the bore, which also maintains the valve carriage and flapper in the closed position, with the flapper in sealing contact with the other retaining member. Bleeding off bore pressure following retraction of the retaining member allows the flapper to lift from the other retaining member and the valve carriage to follow the retracted retaining member, and the end of the retaining member to contact the flapper and push the flapper to the open position.
The valve may include vent means for equalising pressure across the valve closure member prior to the retractable retaining member permitting opening. The vent means may be openable by initial application of fluid pressure, to permit fluid communication across the valve member. Most preferably, the vent means includes a moveable member, such as a sliding sleeve, which initially closes a vent passage but is moveable to open the passage. Preferably also, the moveable member also serves, in its initial position, to lock the retractable retaining member in the retaining position.
The other of the retaining members may be biassed to move the valve closure member to the open position. Alternatively, the valve closure member may be provided with means for biassing the member towards the open position.
According to another aspect of the present invention there is provided a method of completing a downhole string including the steps of:
providing a valve in a tubular string, which valve is capable of holding pressure from both above and below;
running the string into a bore with the valve closed;
securing the string in the bore; and
opening the valve to permit flow of fluid through the string.
Conventionally, in a completion operation, the string is provided with a normally-closed valve which opens in response to higher pressure in the well to permit well fluid to flow into the string. Thus, such valves are not suitable for use as safety valves, and separate safety valves must be provided in the string to safeguard against surges of fluid up through the string when upper end of the string is opened. A valve which will hold pressure from both the sump and surface sides allows for completion testing against the valve and may also serve as a safety valve. In the method of this aspect of the invention top filling may be utilised for filling the string with fluid as it is run into the bore.
According to a further aspect of the present invention there is provided a downhole valve comprising: a curved valve closure member defining a convex face and a seal area on said face; and a valve seat for engaging the seal area.
Preferably, the valve includes a tubular valve body having a main axis and the seal area defines a surface which is substantially perpendicular to said axis.
According to a still further aspect of the present invention there is provided a downhole valve for holding fluid pressure in a first direction, the valve including a non-planar valve closure member defining a peripheral seal surface and a valve seat having a corresponding sealing area, the seal surface and sealing area being substantially perpendicular to said first direction.
It has been found that the sealing capabilities of valves in accordance with this aspect of the invention compare favourably in comparison with valves in which the seal surface simply coincides with the surface of the valve closure member.
Preferably, the valve closure member is a curved flapper, and most preferably the seal surface is provided at the periphery of the convex face of the member.
Preferably also, the sealing area includes a resilient sealing portion.
According to a yet further aspect of the present invention there is provided a ratchet arrangement for downhole apparatus, the arrangement comprising first and second parts, each part defining a toothed face, and a ratch member located between the toothed faces, the parts being axially relatively movable by application of fluid pressure thereto, wherein reciprocal movement of the parts advances the ratch member axially along the toothed faces.
The ratch member may engage a part of another tool or device on reaching an advanced position, and serve to actuate the tool or device or transfer force thereto from one of the parts. In a preferred embodiment the ratch member is utilised to transfer force from the first part to unlock a further part of a valve to permit opening of the valve.
Preferably, the first part defines a piston and is movable on application of fluid pressure thereto, and the first part has a stroke corresponding to the tooth spacing on the toothed faces of the parts such that each pressure cycle will advance the ratch member one tooth. Accordingly, by providing a known number of teeth and knowing the initial position of the ratch member, the ratch member may be moved to a predetermined advanced position by application of a predetermined number of pressure cycles. This feature is useful when used in conjunction with pressure actuated tools for use in completion operations, where pressure is used in, for example, completion testing and setting packers. Using this aspect of the invention, the operation of a particular pressure actuated tool, such as an isolation valve, may be controlled by the ratchet assembly, and will only commence after a predetermined number of pressure cycles, thus accommodating completion testing operations and the setting of packers.
The piston and toothed face of the first part may be integral. Alternatively, the toothed face may form part of a unit, incorporating the other toothed face and the ratch member, which is separable from the tool or device provided in combination with the ratchet assembly.
Preferably, the ratch member comprises first and second portions and a spring portion acting therebetween to urge the first and second portions into engagement with the respective toothed faces. Preferably, the ratch member portions are combined as a single integral part.